This invention is concerned with a set of dark slides for a film holder of a camera which permits an entire zone system of exposures to be made on a single negative.
An object of this invention is a series of dark slides for a camera film holder which permits the economical practice of the zone system of exposure control.
Another object of this invention is a set of dark slides for practicing the zone system exposure procedure in which the number of different slides is held to a minimum.
Another object is to simplify the procedure for determining the densities of negatives obtained from a full range of exposures by making all the exposures on a single negative.
Another object is to simplify testing for density changes when using different developers, different agitation methods and different development times.
Another object is a simplified and economical method of testing new lenses, especially wide angle lenses.
Another object is a simplified and economical method of determining the effects obtained by the use of different filters with an appropriate uniform reflecting surface.
The zone system of exposure is used in black and white scenic, architecture studies and artistic photography. The zone system involves the use of an exposure meter which is set for appropriate film speed to read the luminance of a single value subject area. The exposure meter will indicate an exposure that produces a middle-gray rendering. With conventional negative materials, the negative density produced by this exposure will be optimum for printing as a middle-gray on normal contrast paper. Since this relationship between the indicated exposure and the resulting printed value is known and predictable, it is used to define the midpoint of the image value scale. A middle-gray print value that matches the 18% reflectance gray card is designated value 5. The number of zones in the system may vary but zone 5 is the middle reference and starting point. The lower zones are established with each being one f stop interval smaller than the other and the higher zones are each one f stop exposure increases. When these zones are determined, photographs are taken of the single value subject area starting with the zone 1 exposure which is the minimum exposure and working through the zone 9 or 10 exposure which is the maximum. This required as many as ten separate photographs and ten separate sheets of film.
Since the comparison of the final negatives in a zone system requires consistency in development, problems were faced because as many as ten separate negatives had to be developed. Many developers oxidized rapidly and it has been difficult to develop as many as ten negatives under identical conditions. Therefore, an object of my invention is to make all of the exposures of a zone system on a single negative.
Other objects may be found in the following specification, claims and drawings.